In a motor control apparatus that is coupled to a mechanical load and a motor, vibration may be caused at the resonance frequency in the process of widening the control band in velocity control because of a resonance characteristic that is dependent on the inertia ratio between the mechanical load and the motor and on the rigidity of the machine. To provide stable and highly responsive control, a velocity controller and a frequency characteristic of a filter need to be adjusted such that the vibration at the resonance frequency is reduced and the velocity control band of the motor is enlarged. When a notch filter is used as the filter, it is necessary to adjust the notch frequency, which is the frequency at the center of a band through which input signals are attenuated, and the width (band width) and the depth (attenuation amplitude) for the attenuation. When manually adjusting the frequency characteristic of the filter, an operator is required to operate the mechanical system every time a parameter of the filter and a control gain of the velocity controller are changed and to repeat a process including measurement of a response and determination of whether the response is good or bad.
As a technique for adjusting a frequency characteristic of a filter in accordance with a resonance characteristic of a mechanical system, techniques described in Patent Literatures 1 and 2 are disclosed.
The technique described in Patent Literature 1 includes a vibration-extracting filter having a band-pass characteristic of extracting a vibration component at a predetermined band frequency included in a velocity detection value and uses the magnitude of the amplitude of the extracted vibration component as an evaluation index. The disclosed technique searches for and adjusts the notch frequency on the basis of a gradient method such that this evaluation index is minimized.
In the technique described in Patent Literature 2, the amount of operation having a high frequency component induced by the action of a filter having a high-pass characteristic on the amount of operation output by a controller is applied to a motor. The disclosed technique calculates the resonance frequency by performing Fourier transform on the position detection value induced here and adjusts the notch frequency of a notch filter to the resonance frequency.